In order to allow the healing of lesions to take place at an appropriate rate and without undue pain, an appropriate coverage is placed over the affected area.
It is desirable that this coverage or dressing material constitute ingredients that are all compatible with human or animal skin, and provide, between the environment and the wound, an effective transmission of moisture, while specifically excluding microorganisms from the wound site.
It would be advantageous for such a preparation to be very quick drying, otherwise the home-user or clinician will not have the patience to use it, nor in many cases the opportunity, especially where children or animals are involved.
Another advantageous property of this dressing would be transparency, not only for cosmetic reasons but also to permit inspection of the healing process. Ideally, it should also be capable of being applied as very thin layers so that the resulting dressing would not be cumbersome.
It is also desired that such a dressing be easy to apply and remove, aesthetically pleasing, and non-odourous.
Although such a preparation encompassing all of the above advantages is not presently available, there is a genuine demand for it in many areas including the health care delivery area.
A wide variety of products are currently available on the market in the field of wound dressings. For example, sterile gauze-type dressings that are arranged in strips of various shapes and can be applied directly to the wound, are widely employed in the home for minor injuries. These dressings are mounted on plastic or fabric strips, with an adhesive coating for attachment to skin. Gauze pads are frequently covered with a perforated plastic strip to prevent adhesion of gauze to the wound surface.
U.S. Pat. No. 4,616,644, which issued to Johnson and Johnson Products, discloses a hemostatic adhesive bandage which comprises a pressure-sensitive adhesive-coated backing attached to an absorbent pad covered with a perforated plastic film wound release cover, the wound release cover having a thin coating of polyethylene oxide.
Despite their wide acceptance, the gauze-type dressings are not without their disadvantages. For instance, frequent and sometimes painful changes of such dressings are necessary in order to observe that the healing process is proceeding as desired, and to renew medication. These traditional dressings include two disposable strips called "release sheets" to protect the adhesive, which when removed, present a litter disposal problem. They are usually in strips which are difficult to scale to the size and shape of the individual wounds, especially between fingers and on joints. When applying these preparations to the fingers, it is often necessary to wrap the dressing around several times, so that despite the fact that they are semi-permeable, moisture may not be able to escape adequately leaving the wound site and healthy skin around the wound site swollen and lighter in colour. Moreover, wetting of these gauze-type dressings results in a retained water layer which favours microbial growth. Some manufacturers, such as Johnson and Johnson, have addressed this problem by incorporating an anti-microbial agent, such as benzalkonium chloride, into the gauze pad.
Hydrogels are apparently solid materials, which have some characteristics of animal skin and presumably would provide a good basis for wound dressings. According to Joseph D. Andrade in Hydrogels for Medical and Related Applications, A.C.S. Symposium Series 31, American Chemical Society, 1976, page xi, hydrogels "are three-dimensional networks of hydrophilic polymers, generally covalently or ionically cross-linked, which interact with aqueous solutions by swelling to some equilibrium value". It is known, in some instances, that complexing or interaction between polymer chains occurs by way of hydrogen bonding to form a hydrogel.
It is known to use hydrogel preparations for the clinical treatment of wounds, in particular severe burns. U.S. Pat. No. 4,572,906 discloses a selfsupporting film for use as a surgical dressing in the treatment of severe burns, comprising the hydrogel (15% water) blend of gelatin, chitosan and a compatible plasticizer. The dressing may be removed from the wound by soaking in physiological saline or water.
Canadian Pat. No. 1,176,932 also relates to a hydrogel-based wound adherent film for surgical application consisting of gelatin and a water soluble resin such as polyethylene oxide or polyethylene imine.
Canadian Pat. No. 1,180 622 discloses a hydrogel similar to Canadian Patent No. 1,176,932; however, the combination of gelatin and water soluble resin is in a liquid preparation to be poured by a skilled surgeon directly onto the wound as opposed to existing as a preformed film.
Although these hydrogel preparations provide good protection for wounds, allowing transmission of water vapour from the wound, generally cause less trauma of the skin surrounding the wound after removal (lightness of colour, swelling) compared to conventional dressings, and are transparent allowing the surgeon to monitor the progress of the healing, they do not lend themselves to household use. These hydrogel wound dressings contain, in some instances (Canadian Pat. Nos. 1,180,622 and 1,176,932) ingredients having systemic toxicity such as polyethylene imine. These dressings are therefore suitable for human use only when applied by or under the supervision of a professional for application to large areas of human tissue. For application to smaller areas, self-application may, in some instances, be possible. These preparations are also insufficiently quick-drying for household use.
Other dressings useful in surgical application include those of U.S. Pat. No. 4,524,064 and U.S. Pat. No. 4,243,656.
U.S. Pat. No. 4,524,064 to Nambu discloses a wound covering comprising polyvinyl alcohol, a water-soluble polyhydric alcohol and a high-viscosity water-soluble macromolecular substance. This latter ingredient provides high viscosity for the covering which interferes with migration of the covering components. It is recited in the disclosure of this patent that only high-viscosity macromolecular substances may be used, with the exception of polyvinyl alcohol and a list is given which includes polyacrylic acid. In this instance, polyacrylic acid is employed in a very small amount, and does not provide adhesion to the coating. It is merely added as a viscosity builder.
U.S. Pat. No. 4,243,656 to Walliczek discloses a paint-on liquid dressing for first and second degree burns consisting of acrylic polymer, gelatin, glycerol and water. The acrylic polymer is in the form of an emulsion and is not hydrogel-forming. Accordingly, although gelatin is hydrogel-forming, it merely acts to dilute the emulsion which, when applied to the skin, collapses due to evaporation of water. The emulsion, once collapsed, is not entirely hydrophobic, that is it will absorb some water although it is to such a small extent that it is outside the conventional recognized definition of a hydrogel.
It is known to utilize hydrogel wound dressings for the household treatment of wounds. Two alleged household wound dressings are disclosed in U.S. Pat. No. 3,419,006. These preparations, composed of hydrophilic, polymeric gels are almost entirely water (i.e. approximately 96% water), which leads to poor adhesion to the wound site. They must be reinforced with nylon mesh to prevent breakage. These preparations are primarily intended for use as shoe inserts to prevent chaffing against the skin.
It is an object of this invention to provide an inexpensive wound dressing material that contains only wound compatible ingredients to allow household and clinical use of such a preparation, allows effective transmission of water vapour from the wound site, and provides an effective barrier for the wound against exogenous microorganisms.
It is another object of this invention to provide an aesthetically pleasing, wound dressing material that is relatively quick-drying and transparent, although capable of being made opaque, and is easy to apply to allow self-application or application by an untrained person and similar easy removal.
It is another object of the present invention to provide a skin coating material.